1. Field of the Invention
The present invention relates to power actuated valves and in particular the coupling of the actuator to the valve.
2. Description of the Prior Art
Power actuators are available for many of the valves used in industry. These actuators are frequently powered by electric solenoids and by pneumatics. Hydraulic power is also used as are rotary electric motors. The power actuators are commonly designed to mate with valves that are also sold for manual operation. In power operation there is frequently a good deal of stress on valve stem and stem seal. Since the valve is not necessarily under human observation, a stem sometimes loosens resulting in improper operation and sometimes a lot of undesired spillage.
Both double acting and single acting power actuators are available. The double acting actuator provides controlled power for both on and off operation of the valve. The single acting actuator is normally powered in one direction only and has a spring return. Such actuators are normally designed so that they open a valve under power and shut it by the spring return. Sometimes, however, control systems are set up in reverse. With a power actuator it is not always easy to tell whether a valve is open or shut so it is common to add some kind of indicator. When a control system is set up to operate in reverse, it is necessary that the valve be open when at rest. This change is easily made with ball valves and the like that can be operated through 360.degree. opening and closing at 90.degree. intervals. However, the indicator gets reversed when the valve is rotated 90.degree. to be open at the rest position.